1. Field of the Invention
The invention relates to a substrate support chuck within a semiconductor processing system. More particularly, the invention relates to the use of conductive polymeric pads as part of an electrostatic chuck for retaining a wafer by the Johnsen-Rahbek effect.
2. Description of the Background Art
Substrate support chucks are widely used to support substrates within a semiconductor wafer processing system. A particular type of chuck used in high-temperature semiconductor wafer processing systems, such as high-temperature physical vapor deposition (PVD), is a ceramic electrostatic chuck. These chucks are used to retain semiconductor wafers, or other workpieces, in a stationary position during processing. Such electrostatic chucks contain one or more electrodes imbedded within a ceramic chuck body. The ceramic material is typically aluminum-nitride or alumina doped with a metal oxide such as titanium oxide (TiO.sub.2) or some other ceramic material with similar resistive properties. This form of ceramic is semiconductive at high temperatures.
In use, a wafer rests flush against the surface of the chuck body as a chucking voltage is applied to the electrodes. Because of the conductive nature of the ceramic material at high temperatures, the wafer is primarily retained against the ceramic support by the Johnsen-Rahbek effect. Such a chuck is disclosed in U.S. Pat. No. 5,117,121 issued May 26, 1992.
One disadvantage of using a chuck body fabricated from ceramic is that, during manufacture of the support, the ceramic material is "lapped" to produce a relatively smooth surface. Such lapping produces particles that adhere to the surface of the support. These particles are very difficult to completely remove from the surface. Additionally, the lapping process may fracture the surface of the chuck body. Consequently, as the chuck is used, particles are continuously produced by these fractures. Also, during wafer processing, the ceramic material can abrade the wafer oxide from the underside of the wafer resulting in further introduction of particulate contaminants to the process environment. During use of the chuck, the particles can adhere to the underside of the wafer and be carried to other process chambers or cause defects in the circuitry fabricated upon the wafer. It has been found that tens of thousands of contaminant particles may be found on the backside of a given wafer after retention upon a ceramic electrostatic chuck.
Similarly, substrate support chucks that are used in low-temperature processing (e.g., less than 300 degrees Celsius) may also produce contaminant particles that interfere with wafer processing. Such low-temperature chucks include electrostatic chucks and mechanical clamping chucks which contain wafer support surfaces that are typically fabricated from dielectric materials such as alumina. These types of chucks have also been found to produce particulate contaminants that can adhere to the underside of the wafer during processing.
A commonly assigned U.S. patent application Ser. No. 08/791,941, "Stand-Off Pad for Supporting a Wafer on a Substrate Support Chuck and Method of Fabricating Same", filed Jan. 31, 1997, overcomes the disadvantages of these prior art by the use of a polymeric stand-off pad, which supports a wafer in a spaced-apart relation to the chuck surface. Being less abrasive and more compliant than the chuck surface material, the polymeric pad significantly reduces particulate contamination. This commonly assigned patent application is hereby incorporated by reference.
A Japanese laid-open patent application (Kokai) no. 63-194345 discloses an electrostatic chuck with sheets of a conductive resin material locally arranged on the surface of an insulating film or ceramic material. The capacitance between the wafer and the insulating film is reduced by the increased distance interposed by the thickness of the conductive resin layer. This leads to a chuck with improved charging and discharging time responses, which operates through electrostatic attraction, or coulombic forces, from the charge build-up on an electrode beneath the insulating material.
However, the increased distance between the electrode and the wafer also leads to a correspondingly weaker electrostatic chucking force. Therefore, a need exists in the art for an electrostatic chuck that can avoid an abrasive contact with a wafer, reduce the amount of contaminant particles that may adhere to the backside of a wafer, and allow for a strong chucking force via the Johnsen-Rahbek effect.